Indonesia's supreme court has imposed the death penalty on four members of a nine-person Australian drug-running gang who were appealing against lengthy prison sentences for smuggling heroin out of Bali, officials said today.

Scott Rush, Tan Duc Than Nguyen, Si Yi Chen and Matthew Norman, aged 19 to 23, were originally sentenced to life imprisonment for their roles in a plot to smuggle more than 8kg (about 18lbs) of heroin from the resort island to Australia.

The latter three had their sentences reduced to 20 years by Bali's high court while Rush's life term was upheld.

Prosecutors, who had never sought the death penalty for the four men, appealed against the sentence reductions to the supreme court, while Rush appealed against his sentence.

A supreme court official, Mulyadi, said the judges ruled last month in verdicts that were not announced publicly that the men would face the firing squad. They join the two ringleaders, Andrew Chan, 22, and Myuran Sukumaran, 25, who were sentenced to death at the trial.

The men can still seek a judicial review of the whole trial process and ask for clemency from the president.

Lawyers for the four men just sentenced to death said they had not been informed of the new sentence.

Appeals for two of the remaining three gang members are still pending in the supreme court while the ninth member and only woman, Renae Lawrence, declined to appeal after her initial life sentence was reduced to 20 years on appeal.

Four of the gang were caught at Bali airport in April last year while the remainder were arrested at a nearby hotel preparing another shipment.

Australia's foreign minister, Alexander Downer, told parliament the government would support the clemency appeals.

"In the event of Australians being sentenced to death, it is a policy of the Australian government, and has been for many years, to appeal for clemency," he said. "If these reports are correct, then we will appeal for clemency at the appropriate time to President Susilo Bambang Yudhoyono."